The present invention relates to an ink-jet printer which prints an image onto a print medium held on a rotary drum with ink jetted from a print head, and particularly, to an ink-jet printer in which ink is supplied from an ink tank apart from the print head.
Hitherto, serial-type ink-jet printers are widely spreading. In the serial-type ink-jet printer, a print head and an ink tank of a relatively small capacity are mounted on a carriage, and the carriage is movably attached to a guide bar extending across a paper sheet to be printed. The paper sheet is fed in a direction perpendicular to the guide bar at a constant pitch, and the carriage is moved along the guide bar each time paper sheet is fed by the pitch. During the movement of the carriage, the print head jets ink droplets. In a serial-type color ink-jet printer, a plurality of print heads are employed and are supplied with ink of different colors from the respective ink tanks. The plurality of print heads are beforehand filled with ink when the printer is shipped. In the structure as described above, a color image of A4 size is printed out at a relatively low speed.
Thereto in recent years, a drum rotation type ink-jet printer capable of printing a color image at a high speed has been known. This ink-jet printer includes a rotary drum rotating in one direction and a print head disposed to face a paper sheet held on the rotary drum. The print head has a plurality of line-type nozzle units which are arranged along the peripheral surface of the rotary drum, corresponding to cyan(C), yellow(Y), magenta(M) and black(B). Each nozzle unit has a plurality of ink-jet nozzles disposed across the paper sheet in the axial direction of the rotary drum. This ink-jet printer jets ink droplets from nozzle units in response to image signals to print a color image on the paper sheet rotating together with the rotary drum. In this structure, a color image of A4 size can be printed extremely faster than the above-described serial-type printers.
In this drum-rotation type ink-jet printer, a plurality of ink tanks are placed apart from the print head and store ink of different colors to be supplied to the nozzle units of the print head. Each ink tank is connected to a corresponding nozzle unit via a supply tube, and is filled with ink supplied from an ink supplement bottle detachably attached thereto. The ink is conveyed from the ink tank to an ink pressure chamber of the nozzle unit by a supply pump having a valve function and interposed in the supply tube. At the time of printing, the supply pump is stopped in a valve-open state, and the nozzle unit is driven to jet ink. Upon consumption of ink for jet, ink is supplemented to the ink pressure chamber through the supply tube by a capillary action.
In the above-described drum rotation type ink-jet printer, the nozzle unit is empty when the printer is shipped and is filled with ink at a user side when the printer is used. A foreign matter such as a lump of dried ink may exist in the nozzle unit at the beginning of ink-supply. Thus, ink-jet nozzles of the nozzle unit is apt to be clogged by the foreign matter and the quality of printing carried out by such a nozzle unit is deteriorated.